German Patent No. 195 34 445 C2 discusses a fuel injector which has a nozzle needle that is axially movable in a nozzle body. The nozzle needle can be actuated by a piezoelectric actuator and is held in the closed position by a compression spring. Fuel is supplied by an external source at a freely adjustable pressure. The nozzle needle has a central bore and the actuator concentrically surrounds the nozzle needle and is sealed from the fuel pressure with the aid of sealing surfaces.
A particular disadvantage of the fuel injector from German Patent No. 195 34 445 is that, the sealing surfaces notwithstanding, the lift of the actuator may vary because of the effect of the fuel pressure, to such an extent that an air gap, which is provided between the actuator and the valve needle to compensate for thermal linear deformations, becomes so large that the valve cannot be opened.